Cross-linked polyesters and electrical conductors containing them



Nov. 6, 1945. c. s. FULLER CROSS-LINKED POLYESTERS AND ELECTRICAL CONDUCTORS CONTAINING THEM Filed July 11. 1941 /m/ENTOR Y C. 5. FULL ER er Afro/wey mesfsa-Ntv. s, 194s CROSS-LINKED POLYESTEBS AND ELEC- TBICAL CONDUCTOBS THEM CONTAINING Calvin S. Fuller, Chatham, N. J., signor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application July 1l, 1941, Serial N0. 401,952

14 Claims.

The present invention relates to new compositions of matter having many uses, among them the impregnation of porous materials to form tough, abrasion-resistant bodies. to electrical conductors having fibrous coverings impregnated with these new compositions of matter.

Linear polyesters of high molecular weight, such as those described in United States Patent 2,071,250 to W. H. Carothers, have excellent properties of toughness and flexibility which nt them for many uses. Porous or fibrous materials such as textile fabrics, when thoroughly impregnated with these polyesters possess a remarkable strength, toughness and abrasion-resistance. These desirable properties of the linear polyesters are associated with high molecular weights and particularly with molecular weights sumciently high to impart to the polyester the property of cold drawing. The property of cold drawing appears in microcrystalline linear polyesters when average molecular weights are in the vicinity of 8,000 to 10,000 or above, as determined by the Staudinger viscosity method.

The novel compositions of the present invention are produced by heating polyesters which initially possess molecular weights above the cold drawing point under suitable conditions to produce cross-linking, as by heating them in intimate contact with an organic peroxide, iol' a time sumcient to cause the desired degree ci? cross-limiting. The present invention is concerned primarily with substances produced by the vulcanizaticn ci microcrystalline polyesters which have a denite proportion oi their carbonto-carbon bonds unsaturated. Similar crosslinking through the use of organic peroxides can be achieved, although much less readily, in the case oi fully saturated linear polyesters. The polymers produced by this vulcanization have novel and unique properties. ln the cold, below their crystalline melting points, these compounds are extremely hard and tough. At temperatures above 'their crystalline melting points, the hardness and toughness imparted by their crystallinity becomes lost and they become rubber-like in their properties. They possess an even greater toughness than the cold drawing linear polyesters and are more resistant to hydrolysis.

It is important from the standpoint of imparting desirable mechanical properties to the products of the present invention that these products be microcrystalline, since the hardness and toughness of the product is directly related to It also relates 1 the degree of crystallization. It the polyesters subjected to vulcanization. as described above, are mlcrocrystalline in nature prior to crosslinklng, the crystallinity is retained in the ilnal product. The cross-linking of polyesters which do not crystallize at ordinary temperatures produces brittle gels, rubbery gels or sticky gels depending upon the degree of cross-linking and the degree of linear polymerization prior to crosslinking. Highly crystallized cross-linked polyesters-of suiciently high chain length, on the other hand, are extremely hard and tough. They possess a. definite crystalline melting point" above which the crystalline structure disappears and the substances assume physical properties similar to the uncrystallized substances. Substances ci intermediate degrees ci crystallization possess physical properties intermediate the highly crystallized and the uncrystallized polymers.

The ability of linear polyesters to crystailize depends largely upon the character ot the molecular structure of the portion of the polyester molecule between the ester groups. lhev most readily obtainable oi the polyesters which are capable of crystallizlng above room temperatures are the fully saturated polyesters prepared by the csterication of saturated straight chain dicarboxylic acids ci the general structure with straight chain dihydric alcohols of the general structure ilQ--iGI-le) alu-0H where n and m are integers.

.among the polyesters which tend to remain amorphous in the solid state are those which prepared by the esteriilcation of a saturated straight chain dihyclric alcohol with a dicarboxylic acid containing a relatively large proportion of oleflnic carbon-to-carbon bonds, particularly an acid containing conjugated double bonds or a double hond in the alpha position. Those polyesters prepared from a saturated straight chain glycol and maleic acid, fumarie acid, itaconic acid, citraconic acid or muconic acid as the sole dicarboxylic acid tend to remain amorphous. Each of these acids contains oleiinic double bonds conjugated with either another olelnic bond or a carbon-to-oxygen double bond of a carboxyl group.

Polyesters which contain conjugated olenic carbon-to-carbon bonds and which are nevertheless crystalline to a high degree (and are theredetermined by standard mechanical tests.

fore useful for the purposes of the present in-y vention) may be produced by combining the features of the saturated crystalline polyesters and the unsaturated amorphous polyesters described above. Unsaturated microcrystalline polyesters may be produced yby substituting a dicarboxylic acid containing a conjugated olefinic bond, such as maleic acid, for a portion of the dicarboxylic acid in a mixture of glycol and dicarboxylic acid which, when esterified, would have produced a microcrystalline polyester. The resulting partially saturated copolyester will be amorphous or crystalline depending upon the relative proportion of saturated and unsaturated ingredients. This relationship of crystallization to degree of unsaturation may be better explained by reference to the drawing in which:

Fig. 1 is a curve representing the time required for polyesters of varying degrees of unsaturation to reach an arbitrary hardness when allowed to cool from the molten state at the melting point;

Fig. 2 is a curve representing the relative hardness of polyesters of varying degrees of unsaturation which have been subjected to the same degree of polymerization, and

Fig. 3 represents a piece of insulated wire having a protective covering formed by the method of the present invention.

For the purpose oi plotting the curve shown in Fig. 1 a slight excess of ethylene glycol was reacted with a dicarboxylic acid mixture made up of varying proportions of succinic acid and maleic acid. The glycol and dicarboxylic acids were reacted by being heated at 200 C. while dry, oxygen-free hydrogen was bubbled continuously through the reaction mixture. The reaction was allowed to proceed until samples withdrawn from the reaction mixture indicated that the polyester had reached a predetermined value oi melt viscosity, just short of gelation. Each polyester was then allowed to cool from the molten state under identical conditions and the time was measured which was required for the polyester to pass from the molten state at the melting point to a point at which it possessed an arbitrary hardness as The length of time required to reach an arbitrary hardness is roughly indicative of the time required for the polyester to reach a state in which it possesses a certain degree of crystallization. 'Ihe arbitrary hardness selected is roughly indicative of a certain degree of crystallinity in each polyester. The curve of Fig. 1, therefore, represents the rate at which each polyester containing a certain degree of unsaturation crystallizes from the amorphous state when cooled below its melting point.

It can be seen from Fig. 1 that the fully saturated polyesters crystallize most rapidly, whereas polyesters containing more than 25 per cent to 30 per cent maleic acid crystallize extremely slowly.

The curve shown in Fig. 2 was obtained by preparing polyesters from ethylene glycol, succinic acid and maleic acid in the same manner as described in connection with Fig. 1, by allowing the polyester-forming reaction to proceed until the melt' viscosity of the polyester had reached a predetermined value and then permitting the polyester to cool and crystallize to a stable condition. The hardness of the polyesters containing varying percentages of maleic acid was then measured after 48 hours by standard mechanical tests. The hardness in each case indicates roughly the total amount of crystallization which the polyester is capable of undergoing at room temperature after 48 hours.

It can be seen from Fig. 2 that the hardness decreases rapidly with the addition of substantial amounts of maleic acid. It can also be seen that the degree of ultimate crystallization is correlated roughly with the speed of crystallization indicated in Fig. 1. It has been found that when the polyesters containing ethylene glycol, succinic acid and maleic acid are reacted to a point just short of gelation of the mixture, no crystals can be found, after several days standing, in products prepared from reaction mixtures containing amounts of maleic acid as little as 50 per cent by weight of the total dicarboxylic acid. As less maleic acid is used the products become more crystalline but really hard and tough products appear only after the maleic acid is reduced to about 10 per cent. The toughest products are produced when the maleic acid constitutes between aboutv l per cent and about 5 per cent of the total dicarboxylic acid.

Partially unsaturated microcrystalline polyesters of the type described above, which are capable of being converted into the products of the present invention, and particularly those possessing the property of cold drawing are claimed and more particularly described in the copending application of C. J. Frosch, Serial No. 401,957, filed July 11, 1941.

'Ihe products of the present invention are produced by the peroxide induced cross-linking of this vtype of partially unsaturated polyester lying within the crystallization range. If the molecular weight is sufliciently high in the initial partially unsaturated' polyesterto cause cold drawing, the resulting cross-linked polymer will also possess the property of cold drawing even though it is gelled to a relatively infusible state. In order to eliminate the prolonged procedure involved in the production of polyesters having linear characteristics and having extremely high molecular weights, it may be desirable that the polyesters used for the cross-linking procedure of the present invention have a molecular weight considerably below that which is necessary to impart the property of cold drawing. Even if the molecular weight of the initial polyester is considerably below the cold drawing point, the cross-linking procedure of the present invention may so increase the eiective length of the linear chains in the polyester molecules that the nal product possesses the property of cold drawing with the resultant advantages of greater toughness and flexibility. Even if the resulting cross-linked polymers do not contain linear chains of suiicient length to impart the property of cold drawing, still the cross-linking bonds impart to the resulting product a high degree of toughness and strength.

The partially unsaturated polyesters from which the cross-linked polymers of the present invention are produced have been described in terms of polymers formed by the reaction of ethylene glycol, succinic acid and maleic acid. Analogous results may be obtained using varying proportions of other dicarboxylic acids containing unsaturated bonds together with other types of polyester-forming ingredients.

When unsaturated compounds other than maleic acid are used to form the partially unsaturated polyesters, the amount of unsaturation must be limited in the same manner as described above. The eiective concentration of unsaturation in any polyester for the purposes of the present invention is best measured as `the number of ole iinic bonds in the average polyester molecule (assuming all o! the unsaturated bonds in the initial reactants to remain as unsaturated bonds in the polyester which is produced) divided by the number of atoms in the linear chain of the average polyester molecule. l

For the lpurposes oi. the present invention, a conjugated oleilnic bond is defined as a carbonto-carbon double bond which is conjugated with either another carbon-to-carbon double bond or the.-oxygentocarbon double bond of a carboxyl group or an ester linkage. Both types ot conjugation are known to produce a considerably greater activity than is possessed by an unconjugated oleilnic bond. Hard and tough microcrystalline polyesters suitable for producing the cross-linked polymers of the present invention are obtainedvwhen the number o! conjugated oleiinic bonds is less than about per 400 atoms in the linear chain. This corresponds to the unsaturation in; a polyester produced by esteritying ethylene glycol with a dicarboxylic acid mixture made up of 90 mol percent succinic acid and 10 mol per cent maleic acid. The toughest products are produced when the number oi conjugated cle in excess o! about 2,000 las determined by the Staudinger viscosity method. During the esteriilcation reaction in which the slycol is reacted with the dicarboxylic acids there proceeds simultaneously a moderate heat-induced crosslinklng reaction between the double bonded carbon atoms oi the molecules. However, in the absence oi oxygen this moderate cross-linking does not proceed at a rate suflicient to cause gelation of the polyester before extremely long linear chains can be produced having molecular weights above those necessary to impart the property of cold drawing.

The initial partially unsaturated microcrystalline polyester produced as described above may be thoroughly admixed with an organic peroxide and heated to produce the novel cross-linked polymer of the present invention. Among the suitable compounds capable of inducing cross-linking may be mentioned benzoyl peroxide, acetone peroxide, methyl Cellosolve peroxide, dioxane perovide, ethylether peroxide, fluorenone peroxide, and the drying oil peroxides. The most suitable compound appears to be benzoyl peroxide.

The compound inducing cross-linking may be mixed with the partially unsaturated polyester iin bonds lies between about .5 and about 2 such bonds per 400 atoms in the linear chain. The unsaturation within this range corresponds to that present in polyesters from ethylene glycol. succinic acid and maleic acid, where the maleic acid is present in an amount between about 1 per cent and about 5 per cent or the total acid.

The partiallyy unsaturated polyesters to be cross-linked by the method of the present invention may be prepared by any suitable procedure as illustrated by the preparation ot polyethylene succinate maleate described above. They may be prepared by reacting any glycol capable of forming a crystalline polyester with slightly less than an equimolar proportion oi a mixture of a dicarboxylic acid which is capable or forming a microcrystalline polyester with the glycol employed and a dicarboxylic acid containing oonjugated oleilnic carbon-to-carbon bonds, the proportions of the acids being such that the final product will be microcrystalline as discussed above.

Among the suitable glycols (when combined with the proper dicarboxylic acids) may be mentioned ethylene glycol, hexamethylene glycol, deca-methylene glycol or other straight chain aliphatic glycols oi the general formula H0(CHz)OH where n is an integer. Among the suitable acids (when combined with the proper` glycols) may be mentioned succinic acid, adipic acid, pimelic acid, suberic acid, azeiaic acid, se bacio acidfdecamethylene dicarboxylic acid, duodecamethylene dicarboxylic acid, octadecandiolc kacid or other straight chain aliphatic dicarboxylic acids of the general iorrnula CUOHiCHs) @,CGH

1Where m is au integer. Suitable oleihiic acids are maleic acid, fumarie acid, itaconlc acid and citta como acid.

The reaction mixture may be esterlded in@ out oi contact with oxygen under conditions tendina' to remove the water vapor generated cy the reaction, as by bubbling an inert through the reaction mixture, with or without the emplim cation ci a vacuum, or by the reaction ndxture into a teatri under a vacuum. ldreierably esterincation reaction is a poly-'ester :le produced a meteorites weight mrs in any suitable manner, as by adding the compound as such or in solution to the polyester in the molten or the supercooled stated, by mixing the polyester in finely divided solid form with the compound, or by dissolving the compound and the polyester in a common solvent and subsequently evaporating the solvent.

'I'he amount of organic peroxide employed is not extremely critical. About .1 per cent by weight of benzoyl peroxide or other suitable compound will usually be found sumcient to induce gelation oi! the partially unsaturated polyesters. Smaller fr controlled amounts may be added lf it is not desired that the cross-linking proceed to the gel state. Larger amounts up to l per cent or even 2 per cent by weight of the polyester may be employed so long as the oxidizing action of the compound does not exert a deleterious effect upon the polyester. The mixture of v perature sufficiently high to cause the cross-linking action to proceed. Temperatures above C., preferably in the vicinity of C. or higher, will usually be found satisfactory.

The fact that the partially unsaturated polyesters may be subjected to the prolonged heating operation required to produce molecular weights associated with cold drawing and still retain sumcient unsaturation to permit curing appears to be due to a dierence in the mechanism of heat polymerization and cross-linking by peroxide. Apparently heat polymerization takes place be= tween conjugated double bonds in adjacent mole cules. Therefore, when the unsaturated bonds are sumciently diluted with saturated bondsv so that the probability of an unsaturated hond of one molecule coming into Contact with an un saturated bond oi another molecule becomes very slight, the heat polymerization reaction can place only extremely-slowly. However, the per oxide conversion apparently takes place by the dehydrogenation ci saturated carbon atoms and the manner in which the novel products of the present invention may be prepared Example 1 976.5 grams of ethylene glycol, 87.0 grams -of maleic acid and 1681.5 grams of succinic acid (molecular ratio 1.05:0.05:0.95) were weighed into a balloon flask which was surrounded by an electrically heated furnace maintained at 200 C. The reactants were heated at this temperature for 9 hours with a stream of dry hydro gen gas constantly bubbling through the mixture. After a large portion of the water o' reaction together with a portion of the free glycol had been removed from the reaction mixture by this procedure, the substances remaining in the reaction mixture were of a sulciently high molec ular weight so that continued heating under a vacuum could be carried out without excessive volatilization. The flask and its contents were then subjected to continuous evacuation While allowing sulcient hydrogen to enter the system through a needle valve so as to agitate the reactants and still maintain an absolute pressure of 0.5 centimeters of mercury. At the end of 3 hours, atmosphere pressure was reestablished by the admission of hydrogen and 3 grams of hydroquinone was added to retard subsequent oxidation of the reaction mixture upon exposure to the air. The molten reaction mixture was then poured into trays to cool. The product was a white, brittle, microcrystalline material having a melt viscosity of 162.5 poises at 120 C. A portion of this product was melted and then allowed to supercool to 90 C. at which temperature 1 per cent of nely divided benzoyl peroxide was incorporated by thorough mixing. The resulting mixture was heated or 5 minutes at 150 C. to cause curing or cross-linking. A transparent gel resulted which on cooling quickly` crystallized to a hard, iiexible, opaque product.

Example 2 976.5 grams of ethylene glycol, 87.0 grams of maleic acid and 2082.0 grams of adipic acid (molecular ratio 1.05:0.05:0.95) were reacted in the same manner as the reaction mixture in Example 1 except that the heating under a vacuum was continued for 6 hours in place of 3 hours. The product of this reaction, prior to cross-linking, was a semihard, brittle, microcrystalline product which melted sharply at approximately 45 C. and which had a melt viscosity of about 180 poises at 100 C.` 'I'his product when crosslinked in the manner described in Example 1 resulted in a semihard, flexible, tough, microcrystalline product.

Eample 3 A reaction mixture similar to that employed in Example 1 except that 87.0 grams of fumaric acid were substituted for the maleic acid was subjected to the reaction conditions described in Example 1. The product of this reaction was similar in its physical properties to the product of Example 1 both before and after cross-linking with benzoyl peroxide.

Example 4 976.5 grams of ethylene glycol, 87.0 grams of maleic acid, 1504.5 grams of succinic acid and 282.0 grams of azelaic acid (molecular ratio 1.05:0.05:0.85:0.10) were reacted in the same manner as the reaction mixture of Example 1 prior to cross-linking. The product of this reaction had a melt viscosity oi 190 poises at 120 C.

A portion of this product was melted and allowed to supercool to C., at which temperature 1 per cent by weight of nely divided lauryl peroxide was incorporated by thorough mixing. This mixture upon heating for 5 minutes at 150 C. was converted into a transparent gel which upon cooling quickly crystallized to a semihard, iiexible, tough, microcrystalline product.

\ Example 5 976.5 grams of ethylene glycol, 87.0 grams of maleic acid, 1504.5 grams of succinic acid and 282.0 grams of adipic acid were reacted and crosslinked in the same manner as the reaction mixture in Example 4. The resulting product before and after cross-linking possessed physical properties similar to those of the product of Example d.

Example 6 976.5 grams of ethylene glycol, 87.0 grams of maleic acid, 1504.5 grams of succinic acid and 292.5 grams of phenyl succinic acid were reacted in the same manner as described in Example 4 except that benzoyl peroxide was substituted for the lauryl peroxide in the cross-linking procedure.

The product was similar in its properties to the product of Example 4.

Example 7 A reaction mixture similar to that described in Example 1 except that 2880.0 grams oi sebacic acid were substituted for the 1681.5 grams of succinic acid was subjected to the reaction conditions described in Example l. The product prior to cross-linking was a relatively fusible, brittle, microcrystalline substance which was converted into a tough, exible product by curing with benzoyl peroxide.

Example 8 A reaction similar to that described in Example 1 was carried out except that the heating under a vacuum was continued for 8 hours instead of 3 hours. The product prior to cross-linking was a white, tough, exible microcrystalline material possessing the property of cold drawing and having a melt viscosity of 14,600 poises at C. A portion of this material was melted and allowed to supercool to 90 C. at which temperature 1 per cent benzoyl peroxide was incorporated by thorough mixing. After this mixture was heated for 5 minutes at 150 C. a gel was produced which upon cooling was, converted to a hard, tough, ex ible, microcrystalline product having superior physical properties as compared to the ungelled material.

Example 9 A reaction similar to that described in Example 8 was carried out except that 2880.0 grams of sebacic acid was substituted for the 1681.5 grams of succinic acid. The cross-linked product was similar to that described in Example 8 except that it was less hard.

In the examples given above the unsaturated microcrystalline polymers were prepared by the reaction of a saturated glycol with a saturated dicarboxylic acid and an unsaturated dicarboxylic acid. Obviously, it would be possible to introduce the unsaturation requisite for effective cross-link.

ing by reacting a saturated dicarboxylic acid with a. mixture of a saturated glycol and a glycol containing oleiinic bonds, the proportions and nature of thedngredients being such that a microcrystalline polyester is produced. Similar results could also be obtained by reacting a saturated glycol with a dicarboxylic acid containing both saturated carbon-to-carbon bonds and oleflnic carbon-to-carbon bonds, the relative proportion o! saturatedand unsaturated bonds being such as to cause the resultant polyester to be microcrystalline. Similar results could be obtained by the reaction oi a saturated dicarboxylic acid with a partially unsaturated glycol.

The products described above may obviously be modified in any desired manner as by the addition of pigments, dyes. fillers, plasticizers or other materials which do not detract from the desirable properties oi the polymers. The polymers in the course of their preparation may also be copolymerized with other resin producing substances which may modify the properties of but do not destroy the essential characteristics oi' the polymers of the present invention. Thus any of the polyesters described above may, prior to crosslinking, be mixed with a vinyl compound and the resultant mixture may then have incorporated in it an organic peroxide such as benzoyl peroxide; the mixture may then be heated so as to cause cross-linking and copolymeriaation of the vinyl compound with the partially unsaturated polyester. The amount of vinyl compound employed should be suciently small so that the microcrystalline properties oi the polyester are not destroyed. Suitable vinyl compounds which may be thus employed are styrene, methyl methacrylate, vinyl chloride, vinyl acetate, ethyl acrylate, diphenyl benzene or similar vinyl compounds. Copolymers of this type are claimed and more '.Zully described in the copending' application of C. S. Fuller, Serial No. 401,953, filed July ll, 1941.

Fully saturated polyesters, such as those produced by the esteriiication of saturated straight chain elycols with saturated straight chain dicarboxylic acids may be cross-linked in the same manner as described above for the partially unsaturated polyesters. Thus polyesters such as those described in U. S. Patent No. 2,071,250 may be intimately mixed in any suitable manner with an organic peroxide, such as benzoyl peroxide, and heated at about 150 C. until the cross-linking occurs. When fully saturated polyesters are employed, concentrations below 0.2 per cent by weight of benzoyl peroxide have relatively little effect. With concentrations above 0.5 per cent, however, extensive cross-linking and gelation are produced at temperatures above 100 C. The cross-linking of fully saturated polyesters by the method of the present invention is illustrated by the following example:

Example 10 2 grams of polyethylene succinate having an intrinsic viscosity of 0.52 (as measured with a chloroform solution containing 0.4 gram of polyester per 100 cc. of solution) were dissolved in hot methyl Cellosolve acetate and 0.2 grams of benzoyl peroxide were added to the solution. Clear lms of the solution were formed on metal and heated in an oven at 140 C. The liquid films gelled in 10 minutes. The concentration of benzoyl peroxide necessary to cause gelation is dependent upon the intrinsic viscosity of the polymer employed. In general, the intrinsic viscosity should exceed 0.30.

The cross-linked polymers of the present invention are adapted to many uses. Microcrystalline polyesters, not yet cross-linked, may be mixed with an organic peroxide and used for compression molding in the same manner as other thermosetting resinous substances. The mixture of microcrystalline polyester and organic peroxide may also be subjected to an injection molding procedure and the resulting body may subsequently be heated to a curing temperature. Ii the polyesters of the present invention have been cross-linked to an extent insufficient to produce gelation, they may he converted into a plastic melt which may readily be molded into any deam sired shape. Such plastic cross-linked polyesters also possess a relatively broad supercooling interval so that they wiii not crystallize immediately upon being cooled below their crystalline melting point. n the supercooled state they may therefore be subjected to a molding or stamping procedure which simultaneously forms the mass into the desired shape and induces crystallization. Molding in this manner is more particularly described and claimed in the copending application 0f C. S. Fuller, Serial No.' 401,955, filed July 1l,

The property of the gelled polymers of the present invention of passing from a hard, tough crystalline material into a robbery substance at the crystalline melting point makes them admirably adapted for another type oi' molding procedure. At temperatures above the crystalline melting point the polymers of the present 'invention may be subjected to a considerable degree of physical distortion without the formation of cracks in the material. Thus a body of cross-linked polymer may be heated above its transparency point or crystalline melting point, formed into shape in a mold and cooled while being held in this shape. When the body isagain heated to its crystalline melting point it will return to its original shape due to its rubber-like properties and the release oi crystal forces.

Polyesters which upon cross-linking will possess the property of cold drawingl may be formed into excellent fibres by drawing them into iibre form while they are mixed with benzoyl peroxide and before they have been converted to an infusible state. They may subsequently be completely cured and cold drawn to produce iiexible 'fibres of high tensile strength. The products of the present invention will be found useful for most of the purposes for which the linear superpolymers and other materials of resinous properties are adapted.

As discussed above the polymers of the present invention are adapted to be impregnated into porous or fibrous materials such as textile fabrics, paper, Wood pulp and the like. This impregnation is accomplished by impregnating the polyester in the uncured state into the porous material and subsequently converting the polymer to an infusiblc state by heating in the presence of an organic peroxide. It is desirable, though not necessary, that the initial polyester prior to curing have a melt viscosity not above about 500 poises `at C. so as to permit ready impregnation. A melt viscosity between about poises and about 400 poises at 120 C. is the most desirable.

The molten polymer may be impregnated into the porous article by any suitable method. Because of the low viscosity of the uncured polyester, impregnation takes place fairly readily. The compound used for curing may be incorporated into the impregnated body in any suitable manner. Thus the compound may be thoroughly mixed with the molten polyester immediately prior to impregnation. Alternatively the porous body, as for instance a textile thread or fabric, may prior to impregnation with the polyester be thoroughly impregnated with a solution of the compound and the solvent may be evaporated. Heating of the vimpregnated body containing the curing compound at temperatures-above 100 C., preferably about 150 C., for about 5 minutes `will produce the necessary curing.

The products of the present invention are particul'arly adapted for the impregnation of textile, pulp, paper or other fibrous coverings on electrical conductors. A conductor of this type is illustrated in Fig. 3 which shows a conductor made of a metal wire insulated with a rubber composition and having over the rubber insulation a protective covering of a textile fabric, such as a cotton braid, impregnated with a cross-linked polyester prepared as described above. This type of conductor is particularly suited for the outdoor transmission of electric currents for communication purposes. The toughness of the polymer, the resistance of the polymer to hydrolysis and the more thorough impregnation possible with this type of polymer impart to the impregnated covering an extremely high resistance to the abrasion to which this type of wire is normally subject. v

It has been difcult to find a substance which would be suitable as an impregnant for this type of wire. Up to the present time the common commercial practice has involved the use of asphalts and asphalt-stearin pitch mixtures as saturants and :finishing compounds. These materials have been used because of their relative cheapness and their ability to be melted into comparatively uid liquids for impregnation at relatively low temperatures.

It has been suggested that the linear polyesters of sudciently high molecular weight to possess the property of cold drawing be employed as impregnants for this type of wire. 'Wire coverings impregnated with these materials have been found to have very desirable properties. The wires having textile coverings impregnated with the polymers of the present invention 'possess a considerably greater abrasion-resistance than the coverings impregnated with the linear polyesters.

Moreover, the cross-linked polymers of the present invention have a much greater resistance to hydrolysis than do the linear polyesters and therefore they are much less subject to deterioration upon continued exposure to the weather. This superior resistance to hydrolysis is indicated by the following tests in which polymer samples were maintained in distilled water at 80 C. for a time sucient to cause equivalent loss of flexibility and tensile strength when cooled to room temperature.

Time to Polymer sample *failure It is not necessary that the partially unsaturated polyesters used for impregnating the textile coverings on wire for outdoor use have s. curing compound added to them or that they be purposely cross-linked before the wire is used.

- When wire of this type is impregnated with lmassassin converted partially unsaturated polyesters and is exposed to air and sunlight, cross-linking is induced in the polymer, thus imparting the desirable properties of cross-linking.

The toughness, abrasion resistance, resistance to hydrolysis and good electrical properties of the cross-linked polymers of the present inven tion also render them very desirable for other insulating purposes, as for the impregnation of Example 11 A polymer was prepared according to the procedure of Example l but without the incorporation of benzoyl peroxide or subsequent crossflinking. One thousand grams of this product was pigmented by stirring in 50 grams of carbon black while the polymer was in the molten state. The molten substance was then extruded over a rubber covered wire and a braided textilecovering was then formed over the `wire while the material was still uid, using a textile which had previously been impregnated with a 2 per cent solution of benzoyl peroxide in benzene. Imnie diately after the braiding operation, the wire was passed through a iinishing die and then through a curing oven maintained at '150 C. The wire was then dusted with finely divided mica and allowed to cool. A tough, hard, abrasion-resistant covering was obtained which had good weathering properties.

Example 12 A wire was prepared in the same manner as described in Example 1l using a polymer which was similar except that 2880.0 grams of sebacic acid were substituted for the 1681.5 grams of succinic acid used in its preparation. The resulting covering was similar in its properties except 4that it remained more exlble at low temperatures.

Example 13 The unconverted polymer of Example 9 was pigmented with carbon black and extruded over a rubber covered wire as described in Example l1. A braided cotton covering was then formed over the wire while the polymer was still iluid, using a textile containing no benzoyl peroxide. No curing operation was employed. A tough, hard, abrasion-resistant covering was obtained which had good weathering properties.

Example 14 A polymer was :prepared as described in Example 2 without the incorporation of benzoyl -peroxide and subsequent cross-linking. One thousand grams of this material was heated to 60 C. and 10 grams of benzoyl peroxide together with 50 grams of carbon black were thoroughly incorporated by mixing. This material, heated to 60 C., was employedin a special impregnating device to impregnate the textile braid over a parallel pair of rubber covered drop wire. The wire was then pulled through a nishing die and a curing oven maintained at C., subsequently dusted with finely divided mica and allowed to cool.

Example 100 grains of polyethylene succinate maleate (the maleic acid constituting 'l per cent by weight of the total acid used in the preparation of the polymer) having a melt viscosity of 200 poises at i C. was intimately mixed while hot with 20 grams ci styrene and 3 grams of lamp black. This material was applied in the molten state to a rubber insulated conductor; cotton yarn bearing on its surface a deposit of benzoyl peroxide in amounts suficient to catalyze strongly the polymerization reaction was then braided directiy into thesiluid material over the rubber. The braided conductor was then passed through a smoothing orifice and cured at a temperature of 130 C. for 10 minutes. A tough abrasion-resistant and water-resistant covering was obtained.

Example 17 A cotton fabric was impregnated with molten polyethylene succinate iumarate (prepared with 3 per cent iurnaric acid by weight of the total acid) having a melt 'viscosity of 1,000 poises ai 120 C. and the excess material was scraped ofi with a steel blade. Sheets of this material were uniformly dusted with finely divided benzoyl peroxide in an amount equal to about 0.5 per cent by. weight of the polymer. The impregnated sheets were then stacked in a hydraulic press and pressed together at 120 C. under a pressure of 500 pounds per square inch for l5 minutes. Tough, abrasion-resistant sheets, suit- `able for use as artificial leather, were produced in this manner.

The invention has been described in terms of its specific embodiments but it is apparent that certain modifications will be suggested to those skilled in the art. Such modications are intended to be included within the scope of the present invention which is to be limited only by the scope of the appended claims.

What is claimed is:

1. An infusible insoluble polymer produced by curing, with an organic peroxide, a fusible micro- Y.crystalline dihydroxy aliphatic hydrocarbon-dicarboxy aliphatic hydrocarbon polyester, said polyester possessing suillcient crystallinity and a sufliclent degree of linear growth to impart the property of cold drawing when in the form of thin laments.

2. An infusible insoluble polymer produced by curing, with an organic peroxide, a fusible microcrystalline polyester the molecules of which, aside from the functional end-groups, consist of aliphatic hydrocarbon radicals linked together with ester groups of the structure into linear ester chains, the degree of crystallinity and the degree of linear growth of the polyester being suilicient to impart the property of cold drawing when in the form of ne filaments, said polyester containing less than 5 oleinic bonds per 400 atoms in the linear ester chains, calculated by assuming no cross-linking between molecules at the unsaturated bonds, said polyester containing no other carbon-to-carbon unsaturated bonds.

3. An infusible, insoluble polymer produced by curing with benzoyl peroxide, a fusible microcrystalline dihydroxyalkane-dicarboxyalkane-di carboxyoleiin polyester, the dihydroxyalkane being composed of two hydroxyl groups substituted on the opposite end carbon atoms of a straight chain allsane, the dicarboxyalkane'being cornposed of two carboxyl groups substituted on the opposite end carbon atoms ci a straight chain alkane, the dicarboxyolen and the dicarboxyalkane being so proportioned that the polyester contains less than 5 olefinic bonds per 400 atoms in the linear ester chains, calculated by assuming no cross-linking between molecules at the unsaturated bonds, said fusible polyester possessing sumcient crystallinity and a suilicient degree of l linear growth to impart the property of cold drawing when in the forni oi thin lfilaments.

4. An infusible, insoluble polymer produced by curing, with benzoyl peroxide, a fusible microcrystalline ldihydroxyalizane dicarboxyalkanemaleic acid polyester, the dihydroxyalirane being composed of two hydroxyl groups substituted on the opposite end carbon atoms of a straight chain alkane, the dicarboxyalkane being composed of two carboxyl groups situated on the opposite end carbon atoms of a straight chain allcane, the maleic acid and dicarboxyalkane being so proportioned that the polyester contains less than 5 olenic bonds per liGII1 atoms in the linear ester chains, calculated by assuming no crosslinking between molecules at the unsaturated bonds, said fusible polyester possessing sumcient crystalllnity and a sufilcient degree of linear growth to impart the property of cold drawing when in the form of thin laments.

5. An infusible, insoluble polymer produced by curing, with benzoyl peroxide, a fusible microcrystalline ethylene glycol-succinic acid-maleic acid polyester, the maleic acid and succinic acid l being so proportioned that the polyester contains less than 5 oleflnio bends per 400 atoms in the linear ester chains, calculated by assuming no cross-linking between molecules at the unsaturated bonds, said fusible polyester possessing suficient crystallinity and a suilicient degree of linear growth to impart the property of cold drawing when in the form of thin iilaments.

6. An infusible, insoluble polymer produced by curing, with benzoyl peroxide, a fusible microcrystalline ethylene glycol-sebacic acid-maleio acid polyester, the maleic acid and sebacic acid being so proportioned that the polyester contains g aseaeie the opposite end carbon atoms of a straight chain alkane, the dicarboxyalkane being composed of two carboxyl groups situated on the opposite end carbon atoms of a straight chain alkane, said fusible polyester possessing sulcient crystallinity and a sumcient degree of linear growth to impart the property of cold drawing when in the form of thin filaments.

8. An infusible, insoluble polymer1 identical with the polyester produced by curing, with benzoyl peroxideypolyethylene succinate having an intrinsic viscosity in chloroform greater than .3 and having a sufiicient degree of linear growth to impart the property of cold drawing when in the form of thin filaments.

9. An electrical conductor covered with a layer comprising a fibrous material impregnated with an infusible insoluble polymer produced by curing, with an organic peroxide, a fusible rnicro= crystalline dihydroxy aliphatic` hydrocarbon-dicarboxy aliphatic hydrocarbon polyester, said fusible polyester possessing suicient crystallinity and a suicient degree of linear growth to impart the property of cold drawing when in the form of thin filaments.

10. An electrical conductor covered with a layer comprising textile fabric impregnated with a polymer produced by curing, with benzoyl peroxide, a fusible ethylene glycol-sebacic acidmaleic acid polyester, which fusible polyester possesses the property of cold drawing.

11. An electrical conductor covered with a layer comprising a textile fabric impregnated with an ethylene glycol-sebacic acid-maleic acid polyester, which polyester possesses the property of cold drawing.

12. A shaped body of a normally microcrystalline, normally rigid polymer which, above its crystalline melting point, is a deformable, infusble, rubber-like gel possessing reversible elasticity, said polymer being produced by curing, with an organic peroxide, a fusible, microcrystalline polyester, the molecules of which, aside from the functional end groups, consist of aliphatic hydrocarbon radicals linked together with ester groups of the structure ll o 'unsaturated bonds, said body being crystallized in a shape diferent from that to which the body would return under the inuence of its elasticity when heated above its crystalline melting point.

13. The shaped body described in Aclaim l2 wherein the polymer is produced by curing, with an organic peroxide, a fusible, microcrystalline dihydroxy aliphatic hydrocarbondicarboxy aliphatic hydrocarbon polyester, said polyester possessing sucient crystallinity and a sucient degree of linear growth to impart the property of cold drawing when in the form of thin filaments.

14. The shaped body described in claim 12 wherein the polymer is produced by curing, with benzoyl peroxide, a fusible, microcrystalline ethylene glycol-sebacic acid-maleic acid polyester, the maleic acid and sebacic acid being so proportioned that the polyester contains less than 5 olenic bonds per 400 atoms in the linear ester chains, calculated by assuming no cross-linking between molecules at the unsaturated bonds, said fusible polyester possessing sumcient crystallinity and a sumcient degree of linear growth to impart the property of cold drawing when in the form of thin filaments.

CALVIN S. FULLER. 

